The present invention relates to a display apparatus used in various image data processing apparatus, such as monitors for computer terminals and word processors, and view finders for video cameras.
In display apparatus including those based on plasma display, liquid crystal device, electrochromic device, it is desired to effect multi-level gradational display in order to display high-quality images.
In case of dividing one pixel into a plurality of sub-pixels each capable of binary display, it has been known to form sub-pixels having areal ratios of 20:21:22:23: . . . . By such division, it is possible to effect 2N levels of gradational display by constituting one pixel with N sub-pixels. Such a gradational display method has been disclosed in Japanese Laid-Open Patent Application (JP-A) 1-267519, JP-A 55-46783, EP-A 0219479, Japanese Laid-Open Utility Model Application 61-42591, and U.S. Pat. No. 5,124,695.
On the other hand, a gradational display method utilizing a partial areal inversion in a unit pixel based on an applied electric field and not utilizing areal or spatial division of a unit pixel into sub-pixels as described above, has been disclosed in, e.g., U.S. Pat. Nos. 4,712,877, 4,763,994 and 4,824,218.
The former gradational display method of using sub-pixels can be effected by a simpler drive circuit than the latter gradational display method and is therefor economically advantageous.
FIG. 1 is a schematic view of a pixel including sub-pixels. As shown in FIG. 1, one pixel is divided into three color pixels of R, G and B by vertical boundary lines, and each color pixel (unit pixel) is divided into four sub-pixels having areal ratios of 1:2:4:8 so as to obtain a required number of gradation levels (24=16 in this case). Accordingly, in this case, each color is displayed in 16 levels, and 4096 colors can be displayed in one pixel. This type of division pattern wherein one pixel is divided into three colors of R, G, and B by vertical boundary lines and further divided by horizontal lines, is hereinafter called division pattern A.
However, such a division scheme can cause a problem regarding image quality in some cases. More specifically, in displaying images having continuously changing gradation levels such as photographic images and computer graphic images by using a display device having such a pixel arrangement, an experiment of image processing by the dither method was performed in order to display a more natural image. As a result, an unintended characteristic pattern (linear defect) appeared at a part of changing certain gradation levels. Such a pattern can deteriorate the image quality.
In view of the above-mentioned problem, an object of the present invention is to provide a display apparatus wherein the occurrence of such a xe2x80x9clinear defectxe2x80x9d found to be attributable to a pixel division pattern for a multi-level gradational display is suppressed by a simple re-arrangement
According to the present invention, there is provided a display apparatus comprising a plurality of unit pixels each divided into a least three sub-pixels for displaying a halftone, said at least three sub-pixels having mutually different areas; wherein one sub-pixels among said at least three sub-pixel has a maximum area which does not exceed a total area of the remaining sub-pixels among said at least three sub-pixels.
According to the above arrangement of sub-pixels in a unit pixel, it is possible to suppress a change in gravity center of photo-spots in a pixel and a change in pixel pattern accompanying a display of different halftone or gradation levels. As a result, the linear defect attributable to a pixel division pattern can be suppressed and a continuous gradational display can be smoothly performed.